Light Neutron-rich Nuclei Research Articles

Influence of light neutron-rich exotic nuclei in deciding abundance patterns relevant for explosive nucleosynthesis

Exotic neutron-rich nuclei play an important role in r-process nucleosynthesis. We study the effect of including proper nuclear structure to calculate neutron capture and photodisintegration rates, especially for 19C and 20N, under the aegis of post-form distorted wave Born approximation (FRDWBA). Considering a network of neutron-rich C–N–O isotopes, we show the effect on abundance calculations in a neutrino-driven wind environment of a core-collapse supernova at two critical temperatures T 9 = 3.4 and 0.62. The results are compared for nuclear physics inputs sourced from the FRDWBA, statistical estimates, and standard databases. At temperatures T 9 = 3.4, where alpha capture, or at T 9 = 0.62, where the neutron capture dominates, one can distinguish the effect of accounting for the exotic nature of the nuclei involved. Furthermore, we assess the impact of varying neutron capture and photodisintegration rates involving halo or bubble structures on the abundances within the network.

Alpha clustering in 41, 45, 49Ca* nuclei formed in neutron induced reactions

The light neutron-rich nuclei play a vital role in nucleosynthesis process and the extent of alpha (α) clustering significantly influence the astrophysical rates. Thus, it is significant to explore the α clustering in these nuclei and in the present work, we have studied the α clustering in 41,45,49Ca* nuclei formed in neutron induced reactions within the dynamical cluster decay model (DCM). The results present that with progression towards neutron-rich 45Ca* and 49Ca* nuclei, there is a significant decrease in the α-cluster preformation factor P0. The inclusion of relativistic mean field theory (RMFT) based microscopic temperature-dependent binding energies (T.B.E.) within DCM, give relatively enhanced α-cluster preformation factor for 41,45,49Ca* nuclei compared to the case of macroscopic T.B.E. based upon Davidson mass formula. The cross-section associated with α-cluster emission depicts strong isospin dependence and falls off significantly with increasing neutron number of Ca* nuclei. Further, for the first time, we inculcate the microscopic nuclear potential constructed via folding the standard Fermi form fitted RMFT cluster densities and M3Y nucleon-nucleon interaction within the DCM. The neutron skin thickness of the Ar cluster, complementary to α-cluster, is varied and its effect upon the nuclear interaction potential and α-cluster preformation factor is analysed. The results present that with growing neutron skin of Ar cluster, the α-cluster preformation factor decreases. It explores a strong correlation among the neutron skin thickness and α-cluster preformation factor in light mass 41,45,49Ca* nuclear systems.

Reaction studies with neutron-rich light nuclei at the upgraded SEC Device: Exploring the excited structure of 11Li

The 11Li nucleus is considered the best example of a two-neutron halo nucleus. While the structure of the ground state is well established there is still a significant debate regarding its excited states despite of the multiple experiments realised mainly from the excitation of the ground state of 11Li that is rather complex. We propose a novel approach, to directly feed the different excited states of 11Li by the (t,p) reaction as 9Li has a simpler structure. We will employ a 9Li beam produced at ISOLDE and post-accelerated by HIE-ISOLDE to energies of 7 MeV/u to impinge on a 3H-target located at the upgraded SEC station, this station contains a new particle detection set up: composed of 5 Si-particle telescopes in a pentagon configuration with end caps consisting of 2 CD Si detectors downstream and 1 CD upstream has been prepared to offer the maximum angular coverage and resolution. Geant4 Monte Carlo simulations with the efficiency of the setup is presented in the following proceeding.

Progress of exotic structure studies in light neutron-rich nuclei

不稳定核的奇特结构，例如：集团结构、闯入态等，是放射性核束物理研究的热点方向之一. 直接核反应实验是研究丰中子核奇特结构的重要手段之一. 我们自主研发了适用于放射性束流在质子和氘靶上发生直接核反应实验研究的带电粒子探测阵列. 利用该高精度、大立体角、模块化、多用途的探测阵列，我们在轻丰中子核的奇特结构实验研究方面取得了一系列重要进展. 我们首次从实验上确认了14C的𝜋 型线性链状分子转动带，首次发现了丰中子核16C的π2σ2构型线性链状分子结构, 还发现了14C 的一个共振态可能有“3α 成线性排列”的线链超形变结构. 我们定量研究了12Be，13B等N = 8附近丰中子核的s波和d波闯入强度，结果表明：12Be基态中s 波占19%，远远小于11Be(~80%)，而d波成分却高达57%，是主要的闯入成分；13B基态中的s(d)波闯入成分约为12%(5%)，处于从Be到 C的过渡.

Three-dimensional General-relativistic Simulations of Neutrino-driven Winds from Rotating Proto-neutron Stars

We explore the effects of rapid rotation on the properties of neutrino-heated winds from proto-neutron stars (PNS) formed in core-collapse supernovae or neutron-star mergers by means of three-dimensional general-relativistic hydrodynamical simulations with M0 neutrino transport. We focus on conditions characteristic of a few seconds into the PNS cooling evolution when the neutrino luminosities obey erg s−1, and over which most of the wind mass loss will occur. After an initial transient phase, all of our models reach approximately steady-state outflow solutions with positive energies and sonic surfaces captured on the computational grid. Our nonrotating and slower rotating models (angular velocity relative to Keplerian Ω/ΩK ≲ 0.4; spin period P ≳ 2 ms) generate approximately spherically symmetric outflows with properties in good agreement with previous PNS wind studies. By contrast, our most rapidly spinning PNS solutions (Ω/ΩK ≳ 0.75; P ≈ 1 ms) generate outflows focused in the rotational equatorial plane with much higher mass-loss rates (by over an order of magnitude), lower velocities, lower entropy, and lower asymptotic electron fractions, than otherwise similar nonrotating wind solutions. Although such rapidly spinning PNS are likely rare in nature, their atypical nucleosynthetic composition and outsized mass yields could render them important contributors of light neutron-rich nuclei compared to more common slowly rotating PNS birth. Our calculations pave the way to including the combined effects of rotation and a dynamically important large-scale magnetic field on the wind properties within a three-dimensional GRMHD framework.

Complete set of bound negative-parity states in the neutron-rich nucleus N18

High-resolution gamma-ray spectroscopy of 18N is performed with the Advanced GAmma Tracking Array AGATA, following deep-inelastic processes induced by an 18O beam on a 181Ta target. Six states are newly identified, which together with the three known excitations exhaust all negative-parity excited states expected in 18N below the neutron threshold. Spin and parities are proposed for all located states on the basis of decay branchings and comparison with large-scale shell-model calculations performed in the p-sd space, with the YSOX interaction. Of particular interest is the location of the 0^-_1 and 1^-_2 excitations, which provide strong constrains for cross-shell p-sd matrix elements based on realistic interactions, and help to simultaneously reproduce the ground and first-excited states in 16N and 18N, for the first time. Understanding the 18N structure may also have significant impact on neutron-capture cross-section calculations in r-process modeling including light neutron-rich nuclei.

Neutron capture cross sections of light neutron-rich nuclei relevant for r -process nucleosynthesis

The measurements of neutron capture cross sections of neutron-rich nuclei are challenging but essential for understanding nucleosynthesis and stellar evolution processes in the explosive burning scenario. In the quest of r -process abundances, according to the neutrino-driven-wind model, light neutron-rich unstable nuclei may play a significant role as seed nuclei that influence the abundance pattern. Hence, experimental data for neutron capture cross sections of neutron-rich nuclei are needed. Coulomb dissociation of radioactive ion beams at intermediate energy is a powerful indirect method for inferring capture cross section. As a test case for validation of the indirect method, the neutron capture cross section ( n , γ ) for C 14 was inferred from the Coulomb dissociation of C 15 at intermediate energy ( 600 A MeV). A comparison between different theoretical approaches and experimental results for the reaction is discussed. We report for the first time experimental reaction cross sections of Na 28 ( n , γ ) Na 29 , Na 29 ( n , γ ) Na 30 , Mg 32 ( n , γ ) Mg 33 , and Al 34 ( n , γ ) Al 35 . The reaction cross sections were inferred indirectly through Coulomb dissociation of Na 29 , 30 , Mg 33 , and Al 35 at incident projectile energies around 400–430 A MeV using the FRS-LAND setup at GSI, Darmstadt. The neutron capture cross sections were obtained from the photoabsorption cross sections with the aid of the detailed balance theorem. The reaction rates for the neutron-rich Na, Mg, Al nuclei at typical r -process temperatures were obtained from the measured ( n , γ ) capture cross sections. The measured neutron capture reaction rates of the neutron-rich nuclei, Na 28 , Na 29 , and Al 34 are significantly lower than those predicted by the Hauser-Feshbach decay model. A similar trend was observed earlier for C 17 and N 19 but in the case of C 14 ( n , γ ) C 15 the trend is opposite. The situation is more complicated when the ground state has a multi-particle-hole configuration. For Mg 32 , the measured cross section is about 40 – 90 % higher than the Hauser-Feshbach prediction.

Coulomb dynamical polarization potential and the electric dipole polarizability for weakly bound and neutron-rich light nuclei

In this paper, we present a method to determine the dipole polarizability of light exotic nuclei with a two-body deuteronlike cluster structure. Using the adiabatic approximation, we solve the Schr\"odinger equation for the internal motion of the exotic projectile incident on a heavy target nucleus and express the resulting Coulomb dynamical polarization potential (CDPP) in terms of regular and irregular Coulomb functions. We then obtain a new expression for the dipole polarizability (${\ensuremath{\alpha}}_{0}$) by equating the real part of this CDPP to the classical expression for the polarization potential. The ${\ensuremath{\alpha}}_{0}$ values for many weakly bound light nuclei are calculated and where values are available were found to be in good agreement with those obtained in previous studies using various other methods.

Role of microscopic temperature-dependent binding energies in the decay of Si*32 formed in the O20+C12 reaction

The investigation of fusion reactions involving light neutron-rich exotic nuclei is of paramount significance to understand nucleosynthesis in astrophysical scenarios. It is also estimated as a possible heat source to ignite $^{12}\mathrm{C}+^{12}\mathrm{C}$ reaction and production of x-ray superbursts from accreting neutron star. Recently, the fusion of neutron-rich $^{20}\mathrm{O}$ with $^{12}\mathrm{C}$ target has been studied with measurement of fusion cross-section $({\ensuremath{\sigma}}_{\text{fus}})$. Bass model under predicts the ${\ensuremath{\sigma}}_{\text{fus}}$ and time-dependent Hartree-Fock model also fails to explain the experimental data. To explicate the same, the investigation of $^{20}\mathrm{O}+^{12}\mathrm{C}$ reaction at near barrier energies has been made within quantum mechanical fragmentation-based dynamical cluster-decay model (DCM). Within DCM, the fragmentation potential comprises temperature-dependent Coulomb, nuclear and centrifugal potentials, along with temperature-dependent binding energies (T.B.E.) calculated within the macroscopic approach of Davidson mass formula. Recently, we have explored the temperature-dependence of different nuclear properties and nuclear symmetry energy within microscopic relativistic mean-field (RMF) theory [M. Kaur et al., Nucl. Phys. A 1000, 121871 (2020)]. In the present work, we inculcate the microscopic T.B.E. from RMF theory within DCM and investigate the structure of fragmentation potential for $^{32}\mathrm{Si}^{*}$ formed in $^{20}\mathrm{O}+^{12}\mathrm{C}$ reaction, comparatively for macroscopic (mac) and microscopic (mic) T.B.E. obtained from Davidson mass formula and RMF theory, respectively. The structure and magnitude of fragmentation potential are found to change drastically/notably along with a change in energetically favored/minimized fragments for both choices of T.B.E. The $\ensuremath{\alpha}$ particles $(^{4}\mathrm{He}$, $^{5}\mathrm{He})$ are favored at lower angular momenta in fragmentation profile for mic T.B.E. case only, which is in the agreement with predictions of statistical model results. This change in the nuclear structure embodied via fragmentation potential energy carries its imprints in the preformation probability ${P}_{0}$ of different fragments and affects the contribution of individual light-charged particle (LCP) channel in the ${\ensuremath{\sigma}}_{\text{fus}}$. A comparison of the relative cross-section of different LCP channels toward ${\ensuremath{\sigma}}_{\text{fus}}$ is quite different for both cases of T.B.E. The cross-section of $^{2}\mathrm{H}$ and $^{4}\mathrm{He}$ LCP channels is relatively enhanced for mic T.B.E. compared to mac T.B.E. Among different LCP channels, the $^{5}\mathrm{He}$ channel is the major contributor in ${\ensuremath{\sigma}}_{\text{fus}}$, which is in line with the results of the statistical EVAPOR model. The DCM-calculated ${\ensuremath{\sigma}}_{\text{fus}}$ is in agreement with the experimental data.

High-Momentum Correlated Nucleons, Tensor Blocking, and Nuclear Shell Structure

Studies of light neutron-rich nuclei revealed many new phenomena in nuclear structures and reactions. One of the most important recent discoveries is the change of magic numbers. Traditional magic numbers (2, 8, 20, 28, 50, 128) have been understood by the spin-orbit coupling in the mean-field potential and they provide the base of nuclear shell model. Recently, however, it was found that some of those magic numbers (N=8, 20) disappear in neutron-rich nuclei. On the other hand, new magic numbers (N=6, 14, 16, 32 and 34) emerge in neutron-rich nuclei. In the present paper, it is shown that tensor correlations give notable effects to such new structures. In nuclei a large amount of binding energy is gained by high-momentum correlated pairs of nucleons due to the tensor interaction. Such tensor correlations strongly depend on the configuration space available for exciting the 2p-2h states. When additional neutrons occupy a new orbital, the previously available 2p-2h configurations may be blocked, resulting in a sudden loss of binding energy otherwise gained by the 2p-2h excitations. Such tensor blocking effects enlarge the energy gaps at all the observed new magic numbers.

Study of the Halo Structure for Some Light Neutron-Rich Nuclei Using the Cosh Potential

The radial wave functions of the cosh potential within the three-body model of $$\left({\textrm{Core}+2n}\right)$$ have been employed to investigate the ground state properties such as the proton, neutron and matter densities and the associated rms radii of neutron-rich $${}^{{6}}$$ He, $${}^{{11}}$$ Li, $${}^{{14}}$$ Be, and $${}^{{17}}$$ B exotic nuclei. The density distributions of the core and two valence (halo) neutrons are described by the radial wave functions of the cosh potential. The obtained results provide the halo structure of the above exotic nuclei. Elastic electron scattering form factors of these halo nuclei are studied by the plane-wave Born approximation.

Activation cross section measurement of the 100Mo(α,n)103Ru reaction for optical potential studies

The light neutron-rich nuclei can be synthesized via (α,n) reactions in the so-called weak r-process. The abundances of these species are derived using reaction network calculations. Such a simulation has astrophysical and nuclear physics inputs, one of the most uncertain parameter is the α-nucleus optical potential. (α,n) cross section measurements can be used to evaluate α-optical potentials. For this purpose, the activation cross section measurement of the 100Mo(α,n)103Ru reaction is in progress at Atomki.

Nuclei near the boundary of neutron stability

This article is devoted to the description of the properties of the lightest nuclei with a large excess of neutrons. Light nuclei have always attracted attention due to the wide variety of their properties. While the structural characteristics of medium and heavy nuclei vary fairly smoothly, only single deviations are observed, the structure of light nuclei varies sharply, two neighboring light nuclei are often completely different from each other. This, on the one hand, makes their study a very interesting task, and on the other hand it makes it difficult to identify common trends. Our interest in light neutron-rich nuclei is connected with the desire to observe the characteristic features of nuclei overloaded with neutrons.

Deep Learning for Nuclear Physics

Deep learning is the state-of-the-art pattern recognition method. It is expected to help scientists to discover most relevant features from big amount of complex data. Different categories of deep learning, the best deep neural network architectures for different data structures, the interpretability of black-box models and the uncertainties of model predictions are reviewed in this article. The applications of deep learning in nuclear equation of state, nuclear structure, mass, decay and fissions are also introduced. In the end, a simple neural network is trained to predict the mass of nucleus. We found that the artificial neural network trained on experimental data has low prediction error for experimental data that are held back. Trained with experimental data, the network predictions for light neutron-rich nuclei deviate from Macro-Micro Liquid model, which indicate that there might be new physics missing in the theoretical model and more data are needed to verify this.

Experimental study of intruder components in light neutron-rich nuclei via single-nucleon transfer reaction

With the development of radioactive beam facilities, studies concerning the shell evolution of unstable nuclei have recently gained prominence. Intruder components, particularly s-wave intrusion, in the low-lying states of light neutron-rich nuclei near N=8 are of importance in the study of shell evolution. The use of single-nucleon transfer reactions in inverse kinematics has been a sensitive tool that can be used to quantitatively investigate the single-particle orbital component of selectively populated states. The spin-parity, spectroscopic factor (or single-particle strength), and effective single-particle energy can all be extracted from such reactions. These observables are often useful to explain the nature of shell evolution, and to constrain, check, and test the parameters used in nuclear structure models. In this article, the experimental studies of the intruder components in low-lying states of neutron-rich nuclei of He, Li, Be, B, and C isotopes using various single-nucleon transfer reactions are reviewed. The focus is laid on the precise determination of the intruder s-wave strength in low-lying states.

Total reaction cross sections of neutron-rich light nuclei measured by the COMBAS fragment-separator

Preliminary results of measurements of the total reaction cross sections σR for nuclei 4He, 6He, 8He, 7Li, 8Li, 9Li, 1Li, 11Be, 9Be, 10Be, 11Be, 12Be, 8B, 10B, 11B and 12B nuclei at energy range (10-50) A MeV with 28Si target is presented. The secondary beams of light nuclei were produced by bombardment of the 15N (50 A MeV) primary beam on Be target and separated by COMBAS fragment-separator. In dispersive focal plane a horizontal slit defined the momentum acceptance as 1% and a wedge degrader of 600 μm Al was installed. The Bρ of the second section of the fragment-separator was adjusted for measurements in energy range (10-45) A MeV. The strong absorption model reproduces the A-dependence of ψR, but not the detailed structure. We are comparing our experimental data with predictions of microscopic (dashed line) and strong absorption model, Glauber multiple scattering theory and preliminary results are obtained.

Total reaction cross sections of neutron-rich light nuclei measured by the COMBAS fragment-separator

Preliminary results of measurements of the total reaction cross sections σ R for nuclei 4 He, 6 He, 8 He, 7 Li, 8 Li, 9 Li, 11 Li, 7 Be, 9 Be, 10 Be, 11 Be, 12 Be, 8 B, 10 B, 11 B and 12 B nuclei at energy range (10-50) AMeV with 28 Si target is presented. The secondary beams of light nuclei were produced by bombardment of the 15N (50 AMeV) primary beam on Be target and separated by COMBAS fragment- separator. In dispersive focal plane a horizontal slit defined the momentum acceptance as 1% and a wedge degrader of 600 µm Al was installed. The B ρ of the second section of the fragment-separator was adjusted for measurements in energy range (10-45) AMeV. The strong absorption model reproduces the A-dependence of σ R , but not the detailed structure. We are comparing our experimental data with predictions of microscopic (dashed line) and strong absorption model, Glauber multiple scattering theory and preliminary results are obtained.

Production of light neutron-rich nuclei in multinucleon transfer reactions

In order to produce more unknown light neutron-rich nuclei, multinucleon transfer processes at energies slightly above the Coulomb barrier are investigated within the inclusion of the deformations of interacting nuclei as independent variables of the dinuclear system (DNS) model (improved DNS model). Transfer cross sections 58,64Ni+208Pb and 40Ca+208Pb are calculated and compared with the experimental data, we find the improved dinuclear system model describes the transfer cross sections reasonably. The calculated results showed that protons and neutrons are transferred to be strongly influenced by the potential energy surface, the injection point position of the projectile on the potential energy surface and the dynamical properties of the DNS. The cross sections of new neutron-rich isotopes through the transfer reactions 70Ni+208Pb and 32,36S+238U are estimated by the multinucleon transfer reactions.

Statistical neutron capture in the limit of low nuclear level density

A major barrier in the study of neutron-induced nuclear reactions is the impossibility of direct measurements with short-lived radioactive isotopes. For these exotic nuclei, theoretical inputs such as the photon strength function (PSF) are poorly constrained. At Los Alamos National Laboratory, the Detector for Advanced Neutron Capture Experiments (DANCE) provides direct measurements of $\ensuremath{\gamma}$-ray cascades following neutron capture reactions on stable or long-lived radioactive nuclei. While Hauser-Feshbach calculations can provide reasonable predictions for neutron capture on heavy nuclei, their application to neutron-rich light nuclei with low nuclear level densities and low neutron separation energies is questionable. In this paper, we report on the $\ensuremath{\gamma}$-ray spectra from individual neutron resonances from the $^{96}\mathrm{Zr}(n,\ensuremath{\gamma})$ reaction, with an emphasis on the sensitivity of of the $\ensuremath{\gamma}$-ray spectra to different PSF models. The comparison of the measured $\ensuremath{\gamma}$-ray spectra with predicted spectra does not support the addition of a low-energy enhancement of the size reported in many charged-particle reaction measurements, but the sensitivity of the $\ensuremath{\gamma}$-ray spectra to different PSF models is weak.

First Spectroscopy of the Near Drip-line Nucleus ^{40}Mg.

One of the most exotic light neutron-rich nuclei currently accessible for experimental study is ^{40}Mg, which lies at the intersection of the nucleon magic number N=28 and the neutron drip line. Low-lying excited states of ^{40}Mg have been studied for the first time following a one-proton removal reaction from ^{41}Al, performed at the Radioactive Isotope Beam Factory of RIKEN Nishina Center with the DALI2 γ-ray array and the ZeroDegree spectrometer. Two γ-ray transitions were observed, suggesting an excitation spectrum that shows unexpected properties as compared to both the systematics along the Z=12, N≥20 Mg isotopes and available state-of-the-art theoretical model predictions. A possible explanation for the observed structure involves weak-binding effects in the low-lying excitation spectrum.